This invention relates in general to pivot door type thrust reversers for aircraft turbine engines and, more particularly, to such a thrust reverser having rack and pinion actuation.
Modern aircraft fan-jet engines have a nacelle or shroud surrounding the engine, spaced outwardly from the core engine cowl to define an annular passage or duct for flow of air rearwardly from the outer portion of an enlarged axial flow compressor. In this type of engine, a large proportion of the total thrust is developed by the reaction to the air driven rearward by the fan and the balance results from ejection of the exhaust gas stream from the engine.
Aircraft using gas turbine engines tend to have high landing speeds, placing great stress on wheel braking systems and requiring very long runways. To reduce this braking requirement and permit use of shorter runways, means are now provided in such engines for reversing a major portion of engine thrust during the landing roll. Many different types of thrust reversers have been designed, of varying effectiveness.
With fan-jet engines, it is possible to block and reverse substantially all of the fan flow without excessive stress on the system, since a large part of the flow, core flow, continues through the engine. In some cases, sufficient reverse flow can be obtained by blocking only a substantial portion of the fan flow.
One type of thrust reverser often used in non-fan type turbine engines, uses a pair of large sturdy clam-shell like blocker doors which swing directly behind the jet exit nozzle and diverge forwardly to reverse thrust. This system must be very heavy and strong. Very complex and sturdy actuators are required for this system, which also tends to undesirably direct much of the reverse flow against aircraft structures.
Another type of thrust reverser uses cascade sets in the sidewalls of the engine nacelle with devices for uncovering the cascades to direct air flow through the cascades, which turn the airflow in a forward direction. A portion of the nacelle wall that covers the cascade set in flight is moved rearwardly by a jack screw or rack and pinon gear set, as described by Sawson in U.S. Pat. No. 4,356,973. Typical cascade type reversers include those disclosed by Montgomery in U.S. Pat. No. 4,145,877 and Hom et al in U.S. Pat. No. 3,500,646. While often effective in fan-jet engines, these systems are mechanically complex, requiring a great many cooperating components.
Still another design uses pivotable doors lying in opening in the sidewall of the shroud or nacelle which pivot outwardly while a second set of doors pivot inwardly to block flow of air through the duct and direct it to the outwardly extending doors which direct air flow forwardly. These dual doors are moved independently by a variety of devices, such as the rack and pinon described by Timms in U.S. Pat. No. 4,407,120. Typical of these dual door systems is the system disclosed by Ellis in U.S. Pat. No. 3,612,401. These systems, while useful in fan-jet engines, tend to be heavy and mechanically complex.
Yet another design uses a plurality of pivotable doors located in openings arranged radially around the shroud. Each door pivots so that one end contacts the engine cowl blocking air flow through the annular duct while the other end extends outside the nacelle in a direction directing airflow in a reverse direction. Typical of these are the systems disclosed by Maison et al in U.S. Pat. No. 3,605,411 and Fournier et al in U.S. Pat. No. 4,485,970. These thrust reversers tend to have greater mechanical simplicity than other systems. However, they often require complex actuation systems which may include components extending into the airflow path during normal engine operation and during reverser deployment resulting in undesirable drag.
Thus, there is a continuing need for improved thrust reversing systems for use in aircraft turbine engines, which combine highly effective flow reversal with low cost, light weight, mechanically simple actuation systems that do not impede air flow during normal engine operation and the reverse mode.